1. Field of the Invention
The present invention relates to an exhaust pipe and a method for manufacturing an exhaust pipe.
2. Discussion of the Background
In order to purify injurious substances such as injurious gases contained in exhaust gases discharged from an engine, a catalyst converter is installed in an exhaust gas passage including an exhaust pipe.
In order to improve the conversion efficiency of injurious substances by the catalyst converter, it is necessary to maintain the temperature of exhaust gases and the temperature of the exhaust pipe and the like through which the exhaust gases is allowed to pass at temperatures suitable for activating the catalyst (hereinafter, referred to also as a catalyst activation temperature).
In a previous exhaust gas purifying system, the temperature of the catalyst converter at starting of an engine is lower than the catalyst activation temperature.
Accordingly, it is required that, in an exhaust pipe connected to the engine, the temperature can be raised to the catalyst activation temperature in a short time from starting of the engine.
For example, JP-A 2009-133214 discloses an exhaust pipe including a cylindrical base material made of a metal, and a surface coating layer made of a crystalline inorganic material and an amorphous binder (amorphous inorganic material). The surface coating layer is formed on a circumferential surface of the base material.
It is described that, in the previous exhaust pipe described in JP-A 2009-133214, when the thermal conductivity of the surface coating layer is lower than the thermal conductivity of the base material, the exhaust pipe is excellent in the thermal insulation property. It is described that, as a result, in the previous exhaust pipe described in JP-A 2009-133214, the temperature can be raised to the catalyst activation temperature in a short time from starting of the engine.
The contents of JP-A 2009-133214 are incorporated herein by reference in their entirety.